Engine pumping losses are a serious consideration with more modern engines being designed to lower the power used to turn the engine. New designs coming out of Detroit etc. are using computer controlled cam, ignition and injection timing, and electronic throttles to lower part throttle cruise engine vacuum to lower these losses. The PCM will control a wider than needed overlap of the cams, open the throttle blade wider and using direct cylinder fuel injection make the engine run smoothly at cruise with very low engine vacuum. A new engine design may only have 5" vacuum at cruise where the old engines were efficiently cruising at 15", this increases fuel economy and power for the same amount of fuel burnt, through better efficiency.


Boggles the mind don't it? Five inches at cruise! Wow, who'd a thought it?
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />